   (.orderBy data-frame (into-array cols)))
 
 (defn order-by-cols
-  "根据给定的字段文本列表构造order by操作并调用"
+  "order by columns named by the columns parameter"
   [columns data-frame]
   (.orderBy data-frame (into-array (cols columns data-frame))))
 
 (defn register-udf1
-  "向 SQLContext 中注册 udf ，这个函数适配 java api udf1 。函数返回传入的 SQLContext。"
+  "register a user defined function match java api udf1 return SQLContext."
   [name func data-type sqlc]
   (-> sqlc
       .udf

  sqlc)

(defn register-udf2
  "向 SQLContext 中注册 udf ，这个函数适配 java api udf2 。函数返回传入的 SQLContext。"
  [name func data-type sqlc]
  (-> sqlc
      .udf

  sqlc)

(defn json-rdd
  "convert data frame as json java rdd"
  [data-frame]
  (-> data-frame
      .toJSON
      .toJavaRDD))

(defn read-json
  "read json (file in path or a java rdd) as data-frame"
  [sqlc data-source]
  (-> sqlc
      .read
      (.json data-source)))

(defn write-json
  "save data-frame as json file to path"
  [data-source data-frame]
  (-> data-frame
      .write
